[Drbd-dev] [PATCH 12/23] sd: handle REQ_UNMAP

[hch at lst.de]

On Thu, Mar 30, 2017 at 11:28:32AM -0400, Martin K. Petersen wrote:
> "hch at lst.de" <hch at lst.de> writes:
> 
> Christoph,
> 
> > On Tue, Mar 28, 2017 at 04:48:55PM +0000, Bart Van Assche wrote:
> >> >  	if (sdp->no_write_same)
> >> >  		return BLKPREP_INVALID;
> >> >  	if (sdkp->ws16 || sector > 0xffffffff || nr_sectors > 0xffff)
> >> 
> >> Users can change the provisioning mode from user space from SD_LBP_WS16 into
> >> SD_LBP_WS10 so I'm not sure it's safe to skip the (sdkp->ws16 || sector >
> >> 0xffffffff || nr_sectors > 0xffff) check if REQ_UNMAP is set.
> >
> > They can, and if the device has too many sectors that will already cause
> > discard to fail,
> 
> I'm not sure I understand what you mean by that?

If you manually change the provisioning mode to WS10 on a device that
must use WRITE SAME (16) to be able to address all blocks you're already
screwed right now, and with this patch you can screw yourself through
the WRITE_ZEROES path in addition to the DISCARD path.